This invention relates to quick-acting clamping devices for use, for example, for the firm clamping of tools, workpieces or other members in machine tools.
The invention is particularly concerned with such a clamping device which comprises a transverse piston which is slidably mounted in a housing for movement in a direction transverse to a clamping direction, means including a pressure chamber for applying fluid pressure to the transverse piston, at least one pressure lever bearing at one end against the transverse piston and at the other end against a pressure plate, which is displaceable in the clamping direction relative to the housing, and a clamping piece is acted upon by the pressure plate and projects from the housing, the pressure lever being pivotal between the piston and the pressure plate between an inclined position and an extended position with respect to the clamping direction.
Preferably there are two pressure levers which together form a toggle mechanism and which bear one against each of two opposite sides of a pressure piece, which forms part of the transverse piston and is displaceably seated in the piston for movement in the clamping direction.
The invention also relates to a method of operating such a clamping device.
A quick-acting clamping device constructed in this manner is disclosed in German Offenlegungsschrift (Published Application) No. 23 19 686. With this known quick-acting clamping device, only relatively small distances in the clamping direction can be moved by the clamping piece, since the large inclined positions of the pressure lever or levers which otherwise would be required relative to the extended position would necessitate extra-ordinarily high pressure forces on the piston which pivots the pressure lever or levers from the inclined position to the extended position. The diameter of the piston would also have to be large. With such a quick-acting clamping device, the requirement for high clamping forces on the one hand and the largest possible clamping clearance of the clamping piece on the other hand are therefore mutually contradictory, so that to produce adequately high clamping forces, for example in the clamping of tools or workpieces and other devices in machine tools, hitherto an axial movement of the clamping piece of only 0.3 mm has been achieved.
From German Offenlegungsschrift (Published Application) No. 21 45 643, it is furthermore known, in a quick-acting clamping device of the initially described type, to move the pressure levers beyond the extended position, which is a dead-centre position of the toggle, into a second but only slightly inclined position, in order thereby to achieve locking in the clamped position, without fluid pressure corresponding to the clamping force having to act continually on the piston which pivots the pressure levers. This quick-acting clamping device likewise suffers from the above-mentioned disadvantages.
In both these known quick-acting clamping devices, limit switches are provided for functional control of the device, but monitoring of the clamping force required in the clamped state is not possible by these switches.
It is the main object of the present invention to provide a quick-acting clamping device which ensures both high clamping forces and also a large axial movement of the clamping piece. It is a further object to provide a method of operating such a quick-acting clamping device, by which the control of a predetermined clamping force is possible in a simple manner.